The present patent application describes a process for preparing substituted phenylacetic acids or their esters by reacting substituted benzyl chlorides with carbon monoxide and alcohols or water in the presence of a catalyst and a dipolar aprotic solvent.
Substituted phenylacetic acids and their esters are important intermediates in the pharmaceutical industry and the agrochemical industry.
The synthesis of phenylacetic acids, starting from benzyl chlorides, and the synthesis of phenylacetic esters is described by Colquhoun, Thompson and Twigg (xe2x80x9cCarbonylation, Direct Synthesis of Carbonyl Compoundsxe2x80x9d Plenum Press, New York, 1991, pages 91-97 and 111-119). The reactions of benzyl chlorides with carbon monoxide and water or an alcohol proceed successfully according to this report in the presence of catalytic amounts of compounds of nickel, cobalt, iron, ruthenium, rhodium, or palladium, and with the addition of stoichiometric amounts of a base in order to neutralize the hydrogen halide produced in the reaction.
Owing to the disadvantages of the known processes and the increasing requirement, the object was to find a process which enables substituted or unsubstituted benzyl chlorides to be converted in a simple and economic manner and in high yields to give the corresponding phenylacetic acid derivatives.
This object is achieved by a process for preparing phenylacetic acid derivatives of the formula (I) by reacting benzyl chlorides of the formula (II) 
with a compound of the formula R6OH and with carbon monoxide in a dipolar aprotic solvent in the presence of a catalyst which comprises at least one compound of a transition metal of subgroup VIII of the Periodic Table of the Elements,
where R1, R2, R3, R4, and R5 independently of one another are the following radicals:
a hydrogen or fluorine atom;
a CH2Cl radical;
a HO2CCHxe2x95x90CHxe2x80x94, NCxe2x80x94 or CF3xe2x80x94 group;
an alkyl, alkoxy or acyloxy radical having in each case 1 to 18 carbon atoms; or
a C6-C18-aryloxy, aryl or heteroaryl radical, where, as heteroatoms, 1 to 3 atoms selected from the group consisting of O, N and/or S are present;
a R82P(xe2x95x90O)xe2x80x94, R9C(xe2x95x90O)xe2x80x94, R9OC(xe2x95x90O)xe2x80x94, R9OC(xe2x95x90O)CHxe2x95x90CHxe2x80x94, R10C(xe2x95x90O)xe2x80x94,
R10OC(xe2x95x90O)xe2x80x94, R10OC(xe2x95x90O)CHxe2x95x90CHxe2x80x94, or R102P(xe2x95x90O)xe2x80x94 radical, where R8 is a C1-C4-alkyl radical, R9 is a C1-C18-alkyl radical or hydrogen and R10 is a C6-C18-aryl radical;
or where at least two of the radicals R1, R2, R3, R4, and R5 are linked to one another and form at least one aliphatic or aromatic ring having 5 to 18 carbon atoms.
R6 is hydrogen, a C1-C18-alkyl radical, in particular a C1-C4-alkyl radical, or a C6-C18-aryl radical.
The radicals R1, R2, R3, R4, and R5 are, in particular, independently of one another hydrogen, fluorine, C1-C8-alkyl, or C1-C8-alkoxy, or two of the radicals R1, R2, R3, R4, and R5 are linked to one another and preferably form an aliphatic or aromatic ring having 5 to 10 carbon atoms. Preferably, the radicals R1, R2, R3, R4 and R5 independently of one another are hydrogen, fluorine and C1-C4-alkyl.
The inventive process can be carried out in the presence or absence of an ionic halide.
Usually, the ionic halide is an alkali metal halide, ammonium halide, alkylammonium halide or phosphonium halide, in particular an alkali metal halide or ammonium halide, where halide has the meaning chloride, bromide or iodide, in particular chloride or bromide, preferably chloride.
The ionic halide used can be ammonium bromide, lithium bromide, sodium bromide, potassium bromide, tetrabutylphosphonium bromide, ammonium chloride, dimethylammonium chloride, diethanolammonium chloride, lithium chloride, sodium chloride, potassium chloride, tetrabutylphosphonium chloride, ammonium iodide, lithium iodide, sodium iodide, potassium iodide and/or tetrabutylphosphonium iodide, in particular lithium chloride, ammonium chloride, dimethylammonium chloride, and/or diethanolammonium chloride.
In the case of the inventive process, however, the presence of the ionic halide can also be dispensed with and the process can be carried out in the absence of the ionic halide.
In a particular embodiment of the process, the ionic halide can be used in particular when the catalyst comprises palladium.
The catalyst comprises at least one transition metal compound of subgroup VIII, in particular compounds of palladium, nickel and/or cobalt, preferably compounds of palladium and/or cobalt, particularly preferably palladium compounds.
For the inventive process, a palladium catalyst that contains nickel, cobalt or palladium applied to a support material can also be used. A supported catalyst of this type has the advantage that it may be removed from the reaction mixture in a simple manner, for example by filtration.
When palladium catalysts are used, it has proven useful in a number of cases for the palladium catalyst to comprise at least one palladium(II) compound, in particular PdCl2, PdBr2 or Pd(OAc)2, preferably PdCl2, or at least one palladium(0) compound, in particular Pd2dba3, where dba is dibenzylideneacetone, Pd(P(C6H5)3)4 or Pd(C8H12)2, preferably Pd2dba3.
In a number of cases it has also proved to be expedient that the catalyst additionally contains a ligand, in particular a phosphine compound.
Phosphine compounds coming into consideration, are, for example, a monophosphine, in particular a tri-(C1-C6)-alkylphosphine or a triarylphosphine, or a diphosphine. Triphenylphosphine, tritolylphosphine, bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane or 1,4-bis(diphenylphosphino)butane, in particular triphenylphosphine can be used very successfully.
According to a particular embodiment, the palladium catalyst contains a bis(triphenylphosphine)palladium(II) compound, for example bis(triphenylphosphine)palladium(II) chloride or bis(triphenylphosphine)palladium(II) bromide.
The catalyst is usually used in an amount of 0.00001 to 0.3 mol of transition metal, in particular 0.0001 to 0.2 mol of transition metal, preferably 0.0005 to 0.1 mol of transition metal, per mole of benzyl chloride of the formula (II).
In a multiplicity of cases it is sufficient to carry out the reaction at a CO pressure of 0.5 to 20 MPa, in particular 0.8 to 10, preferably 1.0 to 6 MPa.
Usually, the reaction can be carried out very successfully at a temperature of 20 to 220xc2x0 C., in particular 40 to 200xc2x0 C., preferably 60 to 180xc2x0 C.
Suitable dipolar aprotic solvents are dioxane, tetrahydrofuran, N-(C1-C18-alkyl)pyrrolidone, ethylene glycol dimethyl ether, C1-C4-alkylesters of aliphatic C1-C6-carboxylic acids, C1-C6-dialkyl ethers, N,N-di-(C1-C4-alkyl)amides of aliphatic C1-C4-carboxylic acids, sulfolane, 1,3-di-(C1-C8-alkyl)-2-imidazolidinone, N-(C1-C8-alkyl)caprolactam, N,N,Nxe2x80x2, Nxe2x80x2-tetra-(C1-C8-alkyl)urea, 1,3-di-(C1-C8-alkyl)-3,4,5,6-tetrahydro-2(1H)-pyrimidone, N,N,Nxe2x80x2,Nxe2x80x2-tetra-(C1-C8-alkyl)sulfamide, 4-formylmorpholine, 1-formylpiperidine or 1-formylpyrrolidine, in particular N-(C1-C18-alkyl)pyrrolidone, N,N-di-(C1-C4-alkyl)amide of aliphatic C1-C4-carboxylic acids, 4-formylmorpholine, 1-formylpiperidine or 1-formylpyrrolidine, preferably N-methylpyrrolidone, N-octylpyrrolidone, N-dodecylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 4-formylmorpholine, 1-formylpiperidine or 1-formylpyrrolidine, particularly preferably N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide. Mixtures of the abovementioned dipolar aprotic solvents may also be used.
In the very particularly preferred variant, N-methylpyrrolidone is used as solvent.
When N-methylpyrrolidone is used as solvent, the resulting hydrogen chloride can be isolated as aqueous hydrogen chloride following the reaction and the solvent N-methylpyrrolidone can be reused.
The compound of the formula R6OH, corresponding to an alkyl alcohol or water, can be added in an amount of 0.1 to 50 mol in each case per mole of benzyl chloride of the formula (II). Usually, the reaction is carried out with an amount of alkyl alcohol or water equivalent to 0.2 to 10, in particular 0.5 to 4, preferably 1 to 4, mol per mole of benzyl chloride of the formula (II).
With the use of benzyl chlorides of the formula (II) where at least one of the radicals R1, R2, R3, R4, and R5 independently of one another is a CH2Cl radical, corresponding to the inventive process, phenylacetic acids of the formula (I) are obtained in which at least one of the radicals R1, R2, R3, R4, and R5 independently of one another is a CH2Cl radical. These products are, in accordance with the described process, again benzyl chlorides of the formula (II) and are reacted further in accordance with the described process. Therefore, one mole of benzyl chloride of the formula (II) where at least one of the radicals R1, R2, R3, R4 and R5 independently of one another is a CH2Cl radical, is equivalent to many moles of benzyl chloride, corresponding to the number of CH2Cl groups.
With the use of benzyl chlorides of the formula (II) where at least one of the radicals R1, R2, R3, R4, and R5 independently of one another is a CH2Cl radical and where at least two CH2Cl groups are in the ortho position, in addition to the phenylacetic acids of the formula (I), 3-isochromanone derivatives of the formula (III) are obtained. 
According to a particular embodiment of the inventive process, the benzyl chloride of the formula (II), the catalyst, the dipolar aprotic solvent and if appropriate also the compound R6OH and if appropriate the ionic halide are charged, the CO pressure and temperature are set and then the alkyl alcohol or the water or a mixture consisting of the alkyl alcohol or water and the diprotic solvent is added.
During the reaction intensive mixing of the reaction partners is provided, in order to ensure a rapid reaction course.
The inventive process is suitable both for continuous and batchwise procedure.
The examples below describe the invention without restricting it thereto.